The present invention relates to a reproducing light quantity control method adopted in an optical memory device, in which a light beam is projected on an optical recording medium having a reproducing layer and a recording layer, and a magnetic aperture smaller than a spot diameter of the light beam is generated in the reproducing layer so as to reproduce record marks recorded on the recording layer, for controlling a reproducing light quantity of the light beam projected on the optical recording medium optimum, and a reproducing light quantity control device, and an optical recording medium.
Conventionally, a technology for improving recording density of an optical recording medium by a so-called super resolution effect has been developed. In this method, a light beam is projected on an optical recording medium having a reproducing layer and a recording layer on a substrate, and a magnetic aperture having a smaller diameter than the light spot diameter is generated on the reproducing layer. As an example of such a method, a so-called magnetic super resolution is known.
The magnetic super resolution is a phenomenon in which a high temperature portion of the reproducing layer by the projection of light beam forms, by the magnetic coupling with the recording layer, a magnetic aperture for reading recorded information. In this phenomenon, the temperature distribution of the portion projected by the light beam takes the form of Gaussian distribution. Also, the temperature distribution is influenced by the heat capacity of the recording medium and the environment temperature. For this reason, it is always required to control the aperture size optimum by controlling the reproducing light quantity. Japanese Unexamined Patent Publication No. 63817/1996 (Tokukaihei 8-63817) discloses a device which carries out this control. The following briefly describes the operation of such a device.
FIG. 16(a) shows a mark string recorded on the optical recording medium and the waveform of reproducing signal obtained when the mark string is reproduced. In FIG. 16(a), when a light beam with a certain reproducing light quantity is projected on the optical recording medium, by the Gaussian temperature of the light beam, the temperature of the center of the light beam projected portion becomes high. In this high temperature portion of the reproducing layer, a magnetic aperture xe2x80x9capxe2x80x9d is generated. When the reproducing light quantity is small, the aperture xe2x80x9capxe2x80x9d takes the form of an aperture xe2x80x9cap1xe2x80x9d having a smaller diameter, indicated by a solid line, and when the reproducing light quantity is large, takes the form of an aperture xe2x80x9cap2xe2x80x9d having a larger diameter, indicated by a broken line.
Of the marks recorded on the recording layer, for example, from a long mark 101 larger than the aperture xe2x80x9cap1xe2x80x9d having a smaller diameter, a signal quantity (for example, peak-to-peak amplitude) v1 of a reproducing signal cl is detected, and from a short mark 102 smaller than the aperture xe2x80x9cap2xe2x80x9d, a signal quantity (for example, peak-to-peak amplitude) v2 of a reproducing signal cs is detected. In this manner, the resolving power when reading the record marks varies depending on the size of the aperture xe2x80x9capxe2x80x9d.
The resolving power can be substituted by a ratio v2/v1 which is a ratio of the reproducing signal quantity v1 of the long mark 101 to the reproducing signal quantity v2 of the short mark 102, and the size of the aperture xe2x80x9capxe2x80x9d can be detected from the value of the ratio.
In a graph of FIG. 16(b), the horizontal axis represents the size Pr of reproducing light quantity, and the vertical axis represents an amplitude ratio of long mark and short mark and an error rate. With respect to reproducing light quantity Pr, the error rate of the reproducing data and the reproducing signal quantity ratio v2/v1 vary in the manner as shown in FIG. 16(b). When the error rate of the reproducing data is minimum, the reproducing signal quantity ratio v2/v1 becomes an optimum amplitude ratio, and the reproducing light quantity becomes an optimum reproducing light quantity Pr0.
Thus, in the conventional device, the reproducing light quantity Pr is controlled after deciding the optimum amplitude ratio so that the reproducing signal quantity ratio v2/v1 obtained from the reproducing signal approaches the optimum amplitude ratio. Also, in the conventional device, on the optical recording medium, the long mark 101 and the short mark 102 are pre-recorded, and there are provided (i) a long mark recording region in which long marks 101 are recorded repeatedly and (ii) a short mark recording region in which short marks 102 are recorded repeatedly. The reproducing signal quantity ratio v2/v1 is detected by reproducing respective control patterns of the long mark 101 and the short mark 102 respectively recorded on the long mark recording region and the short mark recording region, and the reproducing light quantity Pr is controlled so that the reproducing light quantity Pr becomes an optimum reproducing light quantity Pr0.
However, generally, because the heat capacity of each optical recording medium is different, in a reproducing light quantity control device, it is required to measure the error rate of reproducing data and the amplitude ratio (reproducing signal quantity ratio v2/v1) of reproducing signal, and determine an optimum amplitude ratio, and set the optimum reproducing light quantity Pr0 everytime a different optical recording medium is installed.
Here, generally, when a bit rate error is 10xe2x88x925, by an error correction technique, a bit error of 10xe2x88x9212 is obtained, which is demanded in a computer memory device. When the bit error rate is on 10xe2x88x925, in order to measure the bit error rate with an error of 1 percent, it is required to detect at least 100 error bits, and carry out measurement so that the number of sample bits is 107. Generally, since the transfer rate of an optical disk is 10 Mbps at the maximum, it takes 1 second at the fastest to measure the number of sample bits. Since one measurement takes 1 second, for example, when the change in error rate is to be measured while changing the reproducing light quantity in 10 levels, it takes 10 seconds to determine the optimum value (optimum amplitude ratio). Namely, it is required to wait at least 10 seconds from installing of the optical recording medium to recording and reproducing of information. As a result, a problem is presented that a high-speed device cannot be realized.
Further, the conventional device also has a problem that control malfunction results when the optical disk (optical recording medium) has a defect or scratch.
For example, when an irregular reproducing signal is generated by a defect or scratch on the optical disk, and as shown by x1 of FIG. 16(c), when the amplitude v2 of the reproducing signal from the short mark 102 becomes large, or as shown by x4, when the amplitude v1 of the reproducing signal from the long mark 101 becomes small, the reproducing signal quantity ratio v2/v1, namely, the amplitude ratio v2/v1 of the reproducing signal becomes excessively large. When the reproducing light quantity control device mistakenly responds to this amplitude ratio, the reproducing light quantity is increased, and the temperature of the recording layer exceeds the curie point. As a result, a problem is presented that the following record marks are destroyed by the defect or scratch. In the worst case, a serious problem is caused that the periodically recorded reproducing light quantity control patterns of the following record marks are destroyed and the reproducing light quantity cannot be controlled.
Also, as shown in x2 of FIG. 16(c), when the amplitude v2 of the reproducing signal from the short mark 102 becomes small, or as shown in x3, when the amplitude v1 of the reproducing signal from the long mark 101 becomes large, the amplitude ratio v2/v1 becomes excessively small. When the reproducing light quantity control device mistakenly responds to this condition, the reproducing light quantity is reduced, and the temperature of the reproducing layer becomes not more than the curie point. As a result, a problem is presented that the aperture of the reproducing layer disappears and the data cannot be reproduced. In the worst case, the reproducing light quantity control pattern cannot be reproduced, and the reproducing light quantity control is disabled.
Namely, when the signal quantity (amplitude) of the reproducing signal is detected, and the reproducing light quantity is controlled in accordance with this detection, the reproducing light quantity control malfunctions due to the defect or scratch. As a result, the record marks following the defect portion or scratched portion are destroyed, and possibly reproducing cannot be carried out.
It is an object of the present invention to provide a reproducing light quantity control method for an optical memory device, for reducing time required to decide an optimum amplitude ratio so as to speed up an operation from installing of the optical memory device to finishing of preparation for recording and reproducing.
In order to realize the above-mentioned object, a reproducing light quantity control method for an optical memory device of the present invention includes the steps of:
(1) recording test data on an optical recording medium;
(2) reproducing the test data recorded on the optical recording medium by changing a reproducing light quantity in a plurality of light quantity values, the reproducing light quantity being a light quantity of when reproducing;
(3) measuring a quality value and a signal quantity of each of a plurality of reproducing signals from the test data at the plurality of light quantity values;
(4) selecting an optimum reproducing signal quantity from a plurality of reproducing signal quantities in accordance with quality values of the plurality of reproducing signals so as to decide a target value of reproducing signal quantity; and
(5) recording the target value on a target value recording region of the optical recording medium.
With this method, once the target value is recorded on the optical recording medium, in the following, when the optical recording medium is installed in the optical memory device, the measuring operation of the error rate can be omitted. Also, after reading the target value recorded in the target value recording region, it is possible to start the control of reproducing light quantity instantly in accordance with the target value thus read, thereby suppressing the error in the reproducing data.
Namely, the transition to the recording-reproducing operation of information data can be made rapidly.
Also, with the above method, when the target value is decided beforehand at the time of shipping the optical recording medium from the factory, and the target value is recorded in the target value recording region, when the optical recording medium shipped is installed in the optical memory device of the user, the transition to the information recording-reproducing operation can be made instantly.
It is another object of the present invention to provide a highly reliable reproducing light quantity control device for an optical memory device capable of preventing recording marks of the recording layer from being destroyed and preventing the aperture generated in the reproducing layer from disappearing even when a reproducing signal quantity from the reproducing light quantity control pattern is mistakenly detected.
In order to achieve the above-mentioned object, a reproducing light quantity control device for an optical memory device of the present invention which projects a light beam on an optical recording medium including a reproducing layer and a recording layer and generates an aperture having a diameter smaller than a light spot diameter in the reproducing layer so as to reproduce information recorded on the recording layer, is characterized by including:
signal quantity detecting section for detecting reproducing signal quantities from marks recorded on the optical recording medium;
control section for controlling a reproducing light quantity of the light beam so that the reproducing signal quantities detected by the signal quantity detecting section approach a predetermined value; and
reproducing light quantity limiting section for limiting the reproducing light quantity not more than an upper limit value so as to prevent a temperature of the recording layer from reaching a temperature which erases the marks.
With this arrangement, the reproducing light quantity projected on the optical recording medium is limited to be not more than a predetermined upper limit value so that the temperature of the recording layer does not reach a temperature which erases the recording marks. Thus, even when the reproducing signal quantity is mistakenly detected due to a defect or scratch on the disk, the recording marks of the recording layer of the optical recording medium are prevented from being destroyed.
Another reproducing light quantity control device for an optical memory device of the present invention which projects a light beam on an optical recording medium including a reproducing layer and a recording layer and generates an aperture having a diameter smaller than a light spot diameter in the reproducing layer so as to reproduce information recorded on the recording layer, is characterized by including:
signal quantity detecting section for detecting reproducing signal quantities from marks recorded on the optical recording medium;
control section for controlling a reproducing light quantity of the light beam so that the reproducing signal quantities detected by the signal quantity detecting section approach a predetermined value; and
reproducing light quantity limiting section for limiting the reproducing light quantity not less than a lower limit value so that a temperature of the reproducing layer reaches a temperature which generates the aperture.
With this arrangement, the reproducing light quantity projected on the optical recording medium is controlled to be not less than the lower limit value so that the temperature of the recording layer reaches a temperature which generates the aperture. Thus, even when the reproducing signal quantity is mistakenly detected due to a defect or scratch on the disk, the aperture from the control pattern is prevented from disappearing, thus realizing a stable reproducing light quantity control in accordance with the reproducing signal quantity.